The present invention relates to a process for the manufacture of chipboards or particle boards by the formation of a layer made up of chips or particles intermingled with heat actuated or curable binders, these particles being those conventionally used in the formation of such particle boards, by means of air screening, prepressing, and subsequent pressing of the layer with heating in a press, such as a single-layer press, a continuously operating press, or the like.
Devices to carry out such processes are conventional. In the apparatus disclosed by German Utility Model No. 7,140,379, chip-like and/or fibrous particles mixed with binders are conveyed through a heated press on a chip layer carrier moving in an operating rhythm, these particles being spread on the layer carrier, while the latter is at rest and the press is closed, by means of a spreading device arranged above the layer carrier, which can be reciprocated for the formation of a chip layer. This apparatus also comprises a device for subdividing the thus-formed layer into sections to be pressed.
Upstream of the heated press in this apparatus, a prepress is arranged for preliminary compression of the chip layer sections formed on the layer carrier, and this prepress is fashioned to be heatable. With such a construction, the preliminarily compressed layer is heated, for example, downstream of the prepress to such an extent that the upper cover and the intermediate layers are normally at a temperature of about 53.degree. to 55.degree. C., the central or core layer is normally at a temperature of about 40.degree. to 43.degree. C., and the lower cover and intermediate layers are normally at a temperature of about 74.degree. to 76.degree. C.
The relatively minor heating of the central or core layer of the prepressed product is a hindrance to shortening the time required for the pressing operation in the downstream single-layer heating and finishing press.
Although the central or core layer could be exposed to high frequency heating, this step is economical only in the case of boards having a thickness of about 15 mm. In addition, manufacturing costs as well as operating expenses are considerably increased by the use of high-frequency supply sources. Thus, high frequency heating is not used in practice for heating the central layer material.